This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Modern society is greatly dependant on the use of hydrocarbons for fuels and chemical feedstocks. Hydrocarbons are generally found in subsurface rock formations that can be termed “reservoirs.” Removing hydrocarbons from the reservoirs depends on numerous physical properties of the rock formations, such as the permeability of the rock containing the hydrocarbons, the ability of the hydrocarbons to flow through the rock formations, and the proportion of hydrocarbons present, among others.
Easily harvested sources of hydrocarbon are dwindling, leaving less accessible sources to satisfy future energy needs. However, as the costs of hydrocarbons increase, these sources become attractive. Recently, the harvesting of oil sands to remove bitumen has become economical. Hydrocarbon removal from the oil sands may be performed by several techniques. For example, a well can be drilled to an oil sand reservoir and steam, hot air, solvents, or a combination thereof, can be injected to release the hydrocarbons. The released hydrocarbons may then be collected and brought to the surface. In another technique, strip or surface mining may be performed to access the oil sands, which can then be treated with hot water or steam to extract the oil. However, this technique produces a substantial amount of waste or tailings that must be disposed. Traditionally in the oil sand industry, tailings are disposed of in tailings ponds.
One process for harvesting oil sands that generates less waste is the slurrified heavy oil reservoir extraction process. In the slurrified heavy oil reservoir extraction process, the entire contents of a reservoir, including sand and hydrocarbon, can be extracted from the subsurface via wellbores for processing at the surface to remove the hydrocarbons. The tailings are then reinjected via wellbores back into the subsurface to prevent subsidence of the reservoir and allow the process to sweep the hydrocarbon bearing sands from the reservoir to the wellbores producing the slurry.
U.S. Pat. No. 5,832,631 to Herbolzheimer et al. discloses one such slurrified hydrocarbon recovery process that uses a slurry that is injected into a reservoir. In this process, hydrocarbons that are trapped in a solid media, such as bitumen in oil sands, can be recovered from deep formations. The process is performed by relieving the stress of the overburden and causing the formation to flow from an injection well to a production well, for example, by fluid injection. A tar sand/water mixture is recovered from the production well. The bitumen is separated from the sand and the remaining sand is reinjected in a water slurry.
International Patent Application No. WO/2007/050180, by Yale and Herbolzheimer, discloses an improved slurrified heavy oil recovery process. The application discloses a method for recovering heavy oil that includes accessing a subsurface formation, from two or more locations. The formation may include heavy oil and one or more solids. The formation is pressurized to a pressure sufficient to relieve the overburden stress. A differential pressure is created between the two or more locations to provide one or more high pressure locations and one or more low pressure locations. The differential pressure is varied within the formation between the one or more high pressure locations and the one or more low pressure locations to mobilize at least a portion of the solids and a portion of the heavy oil in the formation. The mobilized solids and heavy oil then flow toward the one or more low pressure locations to provide a slurry comprising heavy oil, water and one or more solids. The slurry comprising the heavy oil and solids is flowed to the surface where the heavy oil is recovered from the one or more solids. The one or more solids are recycled to the formation, for example, as backfill.
Backfill systems for reinjection of tailings in mining operations fall into two major flow categories. See Cooke, “Design procedure for hydraulic backfill distribution systems,” The Journal of The South African Institute of Mining and Metallurgy, March/April 2001, pp. 97-102 (hereinafter “Cooke 2001”). The first category is a free fall flow and the second category is a full flow or continuous flow.
The free fall systems are categorized by low flow rates such that gravity force is larger than friction force on a slurry, so that the slurry falls freely in the pipe until it reaches the free surface. The advantage of such a system is its tolerance to variations in tailings stream properties, such as solids volume concentration and flow rate. However, the backfilling pipes may often have a short life span. The reasons behind the short pipe life span include the impact damage of slurry freely falling with speeds of up to 45 m/s, high impact pressure when slurry hits the free surface, high erosion rates when slight deviations from vertical occur in free fall region, and excessive pressure in the event of pipeline blockage.
The continuous systems are categorized by slurry occupying the full length of the reinjection well and the pipelines without any area of free fall. The advantage of this method is a much longer pipe life span as the free fall associated modes of pipe wear may be decreased. However, a fairly high backfill flow rate must be maintained so that friction loss is equal or greater than the backfill weight. Such systems may be sensitive to changes in flow rate and slurry rheology. Therefore, friction regulating/augmenting devices such as liners, valves, breaks or, more often, through solids volume concentration regulation are common. However, if the formation in the immediate vicinity of the injection represents a significant resistance to the backfill flow, then a large backpressure will develop which will support the weight of the backfill.
Most modern backfilling systems in mining operations are of the continuous type. Generally, hydraulic backfills are classified as slurries and pastes (See Cooke 2001). Slurries are characterized by a low fraction of small particles or fines, for example, less than about 75 μm, and volume concentrations equal to or less than particle constant contact solid concentration, i.e., the volume concentration at or above which particles start developing permanent contacts with each other. Pastes, on the other hand, have large fines content and volume concentrations exceeding constant contact solid concentration, for example, about 45-50%. Previous art in this area is strongly related to particle size control and slurry distribution systems.
As suggested above, many efforts have been made previously in this area. Among the prior U.S. patents related to the technology disclosed herein, the following non-exclusive list is representative of those efforts: U.S. Pat. Nos. 3,508,407; 4,968,187; 3,340,693; 6,168,352; 3,786,639; 3,440,824; 5,141,365 4,101,333; 3,608,317; 5,340,235; 6,297,295; 6,431,796; 6,554,368; 6,640,912; 6,910,411; 7,069,990; and 7,571,080. Additionally, published U.S. Patent Application Publication Nos. 2007/0197851 and 2008/0179092 are representative of more recent efforts in this area.